Electric cable.



N0. 655,265. Patented `Aug. 7, |900. G. H. NISBETT. ELECTRIC CABLE'.

Y (Applicatiun filed Dec. 28, 1897.)

(No Model.)

vw W15..

UNrTED STATES PATENT OFFICE.

GEORGE II. NISBETT, OF HUYTON, ENGLAND.

ELECTRIC CABLE.

SPECIFICATION forming part of Letters Patent No. 655,265, dated August '7, 1900.

Application led December 28, 1897. Serial No. 663,941. (No model.)

To all whom it 11m/y concern:

Beit known that I, GEORGE H. NIsBETT, engineer, a subject of the Queen of Great Britain, residing'at Huyton, in the county of Lancaster, England, have invented certain new and useful Improvements in Electric Cables, of which the following is a specification.

My invention has reference to the manufacture of electric cables, and more especially to those known as air-space or dry-core 7 cables adapted for use under Water or other external pressures, and more particularly for telegraph and telephone purposes.

In order that telegraph and telephone cables may have as low an electrostatic capacity as possible, it is the practice in insulating the copper conductor to so arrange the insulating material as to touch the conductor only on a part of its circumference or at intervals, and in this Way the conductor is more or less insulated and surrounded by air. Theelectrostatic capacity of air being lower and the insulation resistance higher than that of solid insulators, a conductor is in this Way obtained having both a loW electrostatic capacity and a high insulation resistance. Such cables are commonly made with paper for subterranean Work and then served or covered With a sheath of lead to exclude moisture. They can, however, be insulated With any other suitable materials provided the air-space be left. Now the presence of the air-space before mentioned more or less surrounding the conductor makes the cable very liable to collapse under pressure-asor instance,that to which submarine cables are subjected-this being vespecially likely When softmetals, guttapercha, or such substances are used either for the insulating material or the Waterproof sheathing; and the object and effect of my invention are toprevent such collapses, and this I do by the construction of cable herein described. The obviouseft'ect of such a col lapse of cable if it did not result in the destruction of the cable would at least be to impair its eiiiciency by closing the air-space.

Ina cable of any of the dry-core or airspace types according to my invention there is provided over the conductor a cover consisting of a spiral strip or strips of metal or other strong substances of any suitable shape in cross-section and so arranged and applied as not to press upon the insulated conductor Within and to be mechanically strong enough to withstand a crushing strain from without. Over this spiral coil a solid sheath of Waterproofing material, such as gutta-percha or other suitable substance, is applied, and this sheath is supported by the spiral cover before referred to, and therefore cannot collapse.

The invention is illustrated in the accompanying drawings, in Which-- Figure l is an elevation, partly in section, of one form of the cable. Fig. 2 is a transverse section thereof. Fig. 3 is a View similar to Fig. l of a modification, and Fig. 4. is a crosssection thereof.

In the form shown in Figs. l and 2 the ma-v terial next the conductor a serves both as a support to the conductor in the air-space in which it (the conductor) lies and as a covering by which the air-space is rendered proof against collapse or impairment by pressure from outside-that is to say, it constitutes the part of the cable by which the air-space is made, Which supports the conductor in said air-space, insulates it, and provides the means by which the external pressure tending to collapse the air-space is resisted. The part a in this case by which these ends are attained consists of spiral convolutions of a suitable nonconducting material of triangular or equivalent form, the outer edges of Which touch or nearly touch each other, as shown, while the spaces, or some of them, of the convolutions stand apart and come next to the conductor and serve to carry it.

lThis spiral covering b may consist of ebonite or any lother convenient and suitable analogous material. Outside this covering the cover c, of gutta-percha or other suitable material by which the air-space is rendered Waterproof, is provided, and again outside this are the longitudinal strengthening-Wires d and coverings of jute or the like. The conductor a, as Will be seen, will only touch its insulating supporting-spirals Z7 at a number of points in the direction of its length, their frequency depending upon the size and shape of the triangular spirals o and upon the pitch at which the spirals are Wound.

IOO

A modification under my invention is shown in Figs. Sand hIA. In this case the insulationsupport of the conductor within the cable and the provision of the means of resistance against collapse or impairment due to outside pressure is afforded partly by triangular spiral supports a', of insulating material, and partly by a flat metal spiral ribbon-cover l), the convolutions of which are a certain distance apart and provide flexibility in the cable. The metal spirals and the internal triangular spirals a' are so disposed in relation to each other that the opening between the convolutions of the cover b stand over the outside or backs of the spirals a', and so these openings are closed. Outside these parts the waterprooiiiig-coating c is applied, and again outside this waterproof coating the strengthening outside wires and coverings, as in the cables above described, are provided.

In cables of the air-space type where more than one conductor is employed the whole of the conductors may be insulated and stranded together and placed or inclosed within the covering, giving it its power to prevent collapse and forming the air-space, or the cond uctors may be separate and kept apart within the air-space of the cable with the protective covering surrounding them.

In the manufacture of the cable in some cases the spiral protecting cover is wound on over the core of the cable, while in the other case it may be preferable that the protective covering be made first and the conductor or conductors threaded through it.

In the application of the invention thus far described its use in connection only with cables built on the air-space principle has been set forth; but it is to be stated it maybe usefully applied in cables other than thesei. c., in cables in which by reason either of the arrangement or of the nature of the insulating materials employed such strengthening` or construction to resist external pressures is either desirable or necessary.

What is claimed in respect of the hereindescribed invention isl. In an electric cable, the combination with the outer strengthening and insulating layers and the inner conductor, of an interposed separating-coil ot' substantially-triangularcross-section,snbstantiallyas described.

2. In an electric cable the combination with the outer strengthening and insulating layers and the inner conductor, of an interposed separator comprising ahelically-coiled insulating-support of triangular cross-section having its flat side out and its apex touching the conductor, substantially as described.

In testimony whereof I have hereunto set my hand in presence of two subscribing witnesses.

G. II. NISi3E'l"`.

I'Vitnesses:

J. l?. DA'UDNEY, JAMES MERCER. 

